Blower wheel and method of making same

ABSTRACT

A centrifugal blower wheel is formed from a sheet metal strip having opposite side edges including marginal rim portions extending continuously along the side edges of the strip. The strip has a plurality of longitudinally spaced transverse blades formed therein between the side edges. The blades are connected with the rim portions by integral webs. The blades are formed into an arcuate shape in successive steps. An initial step partially curves the blades and leaves the end portions of the blades adjacent the webs flat. The flat portions are curved in a subsequent step so that the end portions of the blades are work hardened less than if they are successively bent in a plurality of steps. The rim portions are folded between adjacent blades in order to decrease the longitudinal spacing of the blades. The folds are specially formed so that a plurality of bends in each fold are smoothly curved to prevent fracturing of the metal at the bends. The blades have notches formed in their inner edges for receiving the peripheral edges of a pair of discs. The discs have circumferential protuberances adjacent their outer peripheral edges. The protuberances are deformed into contact with one another at their centers to provide each disc with a pair of radially spaced protuberances which are under bending stress and continuously bias the peripheral edges of the discs into firm engagement with the notches.

United States Patent Richard V. Ross Parma Heights, Ohio [211 App]. No.851,319

[22] Filed Aug. 19, 1969 [45] Patented May 18, 1971 73] AssigneeMorrison Products, Inc.

Cleveland, Ohio [72] lnventor [54] BLOWER WHEEL AND METHOD OF MAKINGSAME 13 Claims, 22 Drawing Figs.

Primary Examiner-Leonard H. Gerin Attorney-Meyer, Tilberry & BodyABSTRACT: A centrifugal blower wheel is formed from a sheet metal striphaving opposite side edges including marginal rim portions extendingcontinuously along the side edges of the strip. The strip has aplurality of longitudinally spaced transverse blades formed thereinbetween the side edges. The blades are connected with the rim portionsby integral webs. The blades are formed into an arcuate shape insuccessive steps. An initial step partially curves the blades and leavesthe end portions of the blades adjacent the webs flat. The flat portionsare curved in a subsequent step so that the end portions of the bladesare work hardened less than if they are successively bent in a pluralityof steps. The rim portions are folded between adjacent blades in orderto decrease the longitudinal spacing of the blades. The folds arespecially formed so that a plurality of bends in each fold are smoothlycurved to prevent fracturing of the metal at the bends. The blades havenotches formed in their inner edges for receiving the peripheral edgesof a pair of discs. The discs have circumferential protuberancesadjacent their outer peripheral edges. The protuberances are deformedinto contact with one another at their centers to provide each disc witha pair of radially spaced protuberances which are under bending stressand continuously bias the peripheral edges of the discs into firmengagement with the notches.

mmm 3578.878

SHEET 1 0F 4 INVENTOR. RICHARD 1 R0519 ATTORNEK? PATENIED HAY 1 8 1921saw 2 or 4 J mvsmox Y RICHARD 14 R058 WZJM {50% A TTOR/VE KS PATENTEU an1 8 WI SHEET u or 4 INVENTOR. R/CHARD 1. 17085 ATTORNEYS BLOWER WHEELAND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION This applicationpertains to the art of blowers and more particularly to centrifugalblower wheels formed from a sheet metal strip. Although the invention isparticularly applicable to centrifugal blower wheels formed from a sheetmetal strip and will be described with particular reference thereto, itwill be appreciated that the invention has broader applications and mayalso be used in such environments as radial flow blowers.

Centrifugal blower wheels are commonly formed from a flat sheet metalstrip having opposite side edges which include marginal rim portionsextending continuously along the strip. The rim portions integrallyinterconnect arcuate blades which are formed transversely of the stripbetween its side edges. Integral webs connect the blades with the rimportions. The blades are formed into an arcuate shape by striking thembetween dies. The end portions of the blades adjacent the webs areplaced under considerable stress when they are deformed. Work hardeningof the end portions of the blades often causes cracks in the metal andresults in failure of the blower wheel. It would be desirable to relievehigh stress concentrations and work hardening in the end portions of theblades adjacent the webs.

In forming such blower wheels from a flat sheet metal strip, the rimportions between adjacent blades are commonly folded in order to reducethe longitudinal spacing between adjacent blades. These folds arecommonly struck between two dies to completely flatten the fold.Complete flattening of the bend areas of the folds places the metalunder extreme strain. Both work and age hardening of the folded portionsoften causes crystallization of the metal in the bend areas and thisresults in fracture of the metal so that the blower wheel can no longerbe used. It would be desirable to fold the rim portions in such a mannerthat the stress in the bend areas would be considerably reduced, and sothat a reduction in work and age hardening would considerably reduce thepossibility of fracture.

In assembling blower wheels made from such sheet metal strips, it iscommon to form notches in the inner edges of the blades and to positionthe peripheral edges of a pair of discs within the notches.Circumferential protuberances on the discs are then flattened to forcethe peripheral edges of the discs into firm engagement with the notches.Flattening of the protuberances is done in such a manner that the metalrelieves itself of stress and the peripheral edges of the discs oftenbecome loose in the notches. It would be desirable to deform theprotuberances in such a manner that continual bias would be placed onthe peripheral edges of the discs to keep them in firm engagement withthe notches and eliminate the possibility that the peripheral edgeswould become loose in the notches.

SUMMARY OF THE INVENTION In accordance with the present invention, acentrifugal blower wheel is formed from a sheet metal strip havingopposite side edges including marginal rim portions extendingcontinuously along the strip. A plurality of longitudinally spacedtransverse blades are formed in the strip between its side edges. Theblades are deformed out of the plane of the strip and into an arcuatecross-sectional configuration in successive steps by forming dies. Theblades are first formed into a slight arcuate shape over a major portionof their length and the end portions of the blades are left flat. In asubsequent forming operation, the flat end portions of the blades arealso formed into an arcuate shape. Reducing successive bending steps onthe end portions of the blades reduces work hardening in those areas andalso reduces the amount of bending the end portions of the blades aresubjected to. The end portions of the blades are connected with the rimportions by integral webs of sheet metal and forming of the blades inthe manner described reduces crystallization of the metal at the endportions of the blades and substantially reduces fracture of the metalin those areas.

In accordance with another aspect of the invention, the rim portions ofthe strip are folded between adjacent blades in order to reduce thelongitudinal spacing between blades. These folds are formed so that thebend areas of the folds are smoothly curved and fatigue fracturing ofthe metal in the bend areas is substantially reduced.

In accordance with still another aspect of he invention, the blades havenotches formed on their inner edges for receiving the peripheral edgesof a pair of discs. Each of the discs has a circumferential protuberanceformed therein adjacent the outer peripheral edges. The protuberancesare deformed so that they move into contact with one another near theircenters to define a pair of radially spaced smaller protuberances oneach disc. The metal in the two protuberances is under bending stresswhich constantly biases the peripheral edges of the discs into firmengagement with the notches and the metal cannot relieve itself to causethe peripheral edges to become loose in the notches.

It is a principle object of the present invention to provide an improvedblower wheel in which fracturing of the metal from which the blower isformed is substantially reduced by reducing stresses and work hardeningin certain areas.

It is another object of the present invention to provide an improvedmethod of forming a blower wheel from a sheet metal strip so thatfracture of the metal in the strip is substantially reduced in certainareas by reducing high stress concentrations and work hardening.

It is also an object of the present invention to provide a blower wheelwith a pair of discs which have their peripheral edges under constantbiasing engagement with notches formed in blades.

It is a further object of the present invention to provide an improvedmethod of assembling a pair of discs to the interior of a cylindricalblower wheel.

BRIEF DESCRIPTION OF THE DRAWING The invention may take physical form incertain parts and arrangements of parts, a preferred embodiment of whichwill be described in detail in this specification and illustrated in theaccompanying drawings which form a part hereof.

FIG. 1 is a top elevational view of a sheet metal strip which is used informing the improved blower wheel of the present invention;

FIG. 2 is a perspective view of a bottom forming die used to deformblades into an arcuate shape from the sheet metal strip of FIG. 1;

FIG. 3 is a perspective view of an upper forming die used in cooperationwith the bottom die of FIG. 2 to deform arcuate blades from the sheetmetal strip of FIG. 1;

FIG. 4 is a perspective view of a portion of a blade strip after formingthe blades with the dies of FIGS. 2 and 3;

FIG. 5 is a cross-sectional view looking in the direction of arrows 5-5of FIG. 4;

FIG. 6 is a cross-sectional view looking in the direction of arrows 6-6of FIG. 4;

FIG. 7 is a perspective view of a bottom forming die which is used toprovide a more pronounced arcuate curvature to the blades;

FIG. 8 is a perspective view of an upper die used in cooperation withthe bottom die of FIG. 7 to provide a more pronounced arcuate curvatureto the blades;

FIG. 9 is a perspective view of blades after final forming with the diesof FIGS. 7 and 8;

FIG. 10 is a cross-sectional view looking in the direction of arrows10-10 of FIG. 9;

FIG. 11 is a cross-sectional view looking in the direction of arrows11-11 of FIG. 9;

FIG. 12 is a partial top plan view of an edge portion of a blade stripshowing successive formation of folds;

FIG. 13 is a side elevational view of a blade strip showing successiveformation of folds;

FIG. 14 is a cross-sectional view looking in the direction of arrows14-14 of FIG. 12;

FIG. is a cross-sectional view looking in the direction of arrows 15-15ofFIG. 12;

FIG. 16 is an enlarged end elevational view of a final fold formed inthe edge of a blade strip;

FIG. 17 is an enlarged end view of a first bend formed in an edgeportion of a blade strip to produce a fold;

FIG. 18 is an enlarged end view ofa deformed bend formed in an edgeportion of a blade strip to produce a fold;

FIG. 19 is an enlarged end view of a further deformed bend formed in anedge portion ofa blade strip to produce a fold;

FIG. 20 is a fragmentary cross-sectional view of a blower wheel and apair ofsupporting discs;

FIG. 21 is a view similar to FIG. 20 showing the configuration of thesupporting discs after deformation; and

FIG. 22 is a partial cross-sectional view of the deformed portion of thediscs of FIG. 21.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings,wherein the showings are for purposes of illustrating preferredembodiments of the invention only and not for purposes of limiting same,FIG. 1 shows flat sheet metal strip A which is used to construct acentrifugal blower wheel in accordance with the present invention. Sheetmetal strip A includes opposite side edges 12 and 14. Adjacent sideedges 12 and 14, sheet metal strip A has marginal rim portions 16 and 18extending continuously along the side edges of the strip. Side edges 12and 14 of strip A have outwardly extending longitudinally spaced tabs 20thereon for cooperation with spacing and holding devices in subsequentforming operations of strip A. A plurality of transverse slits 22 areformed in strip A transversely thereof between rim portions 16 and 18. Aplurality of longitudinal slits 24 are formed in strip A atlongitudinally spaced intervals adjacent rim portions 16 and 18.Longitudinal slits 24 extend from the ends of transverse slits 22 towardthe ends of an adjacent transverse slit and terminate short thereof. Atthe transverse center of strip A, notches 28 are formed and intersecttransverse slits 22. Transverse slits 22 and longitudinal slits 24define a plurality of blade-forming sections 30 in strip A.Blade-forming sections 30 are integrally connected with rim portions 16and 18 by webs 32.

Strip A is fed longitudinally through a forming machine in incrementalsteps in a known manner. The machine includes a bottom forming die B andan upper forming die C. Upper forming die C vertically reciprocates inthe machine as strip A is stopped at the end of each of its incrementalmovements. Bottom forming die B includes an upper arcuate surface 34having substantially triangular flattened areas 36 and 38 at the top endportions thereof. Upper forming die C has a lower arcuate surface 40shaped to correspond with arcuate surface 34. Arcuate surface 40includes flattened portions like those at 36 and 38 on arcuate surface34. Upper forming die C is positioned vertically above bottom formingdie B in the forming machine. A blade-forming section 30 is positionedover bottom forming die B and upper forming die C is positionedvertically above bottom forming die B. Downward movement of upperforming die C causes a blade-forming section 30 to be gripped betweenarcuate surfaces 34 and 40 so that a blade-forming section 30 conformsto the arcuate shape of arcuate surfaces 34 and 40. Strip A is fedlongitudinally through a forming machine in successive increments sothat each blade-forming section 30 is successively formed to an initialarcuate shape between dies B and C. Complete forming of blades 30 totheir final desired arcuate shape in only one step requires an extremelypronounced draw which would often fracture the metal in blade-formingsections 30. Therefore, the initial forming of blade-forming sections 30to an arcuate shape provides only around one-half the desired arcuatecurvature. Flattened areas 36 and 38 on arcuate surface 34, andcorresponding flattened areas on arcuate surface 40 leave the endportions of blades 30 with flattened areas 42 adjacent webs 32.Flattened portions 42 are substantially unworked and unbent in the firstforming operation between dies B and C. The first forming operationperformed on blade sections 30 provides the blades with inner and outertransverse edges 44 and 46 respectively.

As strip A continues longitudinal movement through a forming machine, asecond pair of dies provide the final desired arcuate curvature toblades 30. A bottom forming die D has an arcuate upper surface 50 andupper die E has a lower arcuate surface 52 shaped correspondingly witharcuate surface 50. Arcuate surfaces 50 and 52 are much more pronouncedthan arcuate surfaces 34 and 40 on initial forming dies B and C. Inaddition, final forming dies D and E do not have any flattened portionssimilar to those at 36 and 38 on die B. With upper die E positionedabove die D for vertical reciprocation, a blade section 30 is positionedover die D and die E moves vertically downward to grip a blade section30 between surfaces 50 and 52, and cause blade section 30 to.

conform with the arcuate curvature of arcuate surfaces 50 and 52. Inthis forming operation, flattened areas 42 at the end portions of bladesections 30 are provided with an arcuate curvature corresponding to thecurvature of the major portion of blade sections 30. In this finalforming operation, blade sections 30 are provided with a very pronouncedarcuate curvature and inner edges 44 extend downwardly from the plane ofsheet A at substantially right angles thereto. By leaving flattenedareas 42 at the end portions of blades 30 adjacent webs 32 in the firstforming operation, the end portions of blades 40 are work hardenedconsiderably less than if they were bent successively along with themajor portions of blade sections 30. In addition, the degree of bendingin the end portions of blades 30 adjacent webs 32 is not as pronouncedbecause most of the desired bending is accomplished in the first formingoperation within the inner or lower portion of each blade section 30.This manner of deforming blade sections 30 into their desired arcuateshape considerably relieves stress concentrations at the end portions ofblades 30 adjacent webs 32 and also reduces work hardening of the metalin those areas. It has been found that this substantially reducesfracture of the metal at the end portions of the blades 30 adjacent webs32. In the final forming operation, the end portions of blades 30adjacent webs 32 are given the same arcuate shape as the major portionof blade sections 30 as shown in FIGS. 10 and 11.

Subsequent to the forming of blade sections 30 into their arcuatecross-sectional shape, rim portions 16 and 18 are folded overintermediate tabs 20 and blades 30 in order to decrease the longitudinalspacing of blade sections 30. In accordance with the invention, bladestrip A is moved longitudinally through a deforming machine whileholding dies J and K engage the upper surface of rim portion 16 andportions of adjacent tabs 20 as shown in FIG. 12. Holding dies J and Kengage the top surface of rim portions 16 loosely so that the metal inrim portion 16 and tabs 20 may slide relative to the bottom surfaces ofholding dies J and K. While holding dies J and K are in slidingengagement with the upper surface of rim portion 16 as shown in FIG. 12,a vertically movable pin 62, which extends transversely of rim portion16, moves vertically upward into engagement with the bottom surface ofrim portion 16 intermediate holding dies J and K. This vertically upwardmovement of pin 62 forms an inverted U-shaped bend 64 as shown in FIG.13. This formation of inverted U-shaped bend 64 draws adjacent tabs 20toward one another and decreases the spacing between adjacent bladesections 30. As shown in FIG. 14 with respect to holding die J, thebottom comer edge of holding die J is curved as at 66 and the insidebottom edge of die K is similarly curved. These curved portionsofholding dies J and K, which engage rim portion 16, impart a desiredcurvature as at 70 and 72 to the connecting areas between U-shaped bend64 and rim portion 16. The bottom portions of dies J and K which extendbetween adjacent tabs 20 are provided with an extension 74 as shown onlywith references to die J in FIG. 15. As pin 62 moves vertically upwardin forming U-shaped bend 64, tabs 20 move toward one another and theirinner edges engage projection 74 on holding dies J and K in order toimpart a desired spacing between adjacent tabs and to insure formationof U-shaped bend 64 at substantially the center between adjacent tabs20. Subsequent to formation of inverted U-shaped bend 64, as strip Acontinues to move longitudinally through a deforming machine, avertically movable spacer 76 moves upwardly between adjacent tabs 20between which inverted U-shaped bend 64 has been formed. Spacer 76maintains a desired spacing between adjacent tabs 20 while U-shaped bend64 is struck with a deforming die 78 as shown in FIG. 13. Deforming die78 moves vertically downward sharply to strike the curved portion ofinverted U-shaped bend 64 and causes the curved portion of bend 64 tobreak at its center and become a substantially heart-shaped deformation82. As strip A continues to move longitudinally through a deformingmachine, a subsequent deforming die 84 strikes heart-shaped deformation82 and deforms it into a flattened heart-shaped deformation 86. Finally,a final deforming die 90 strikes deformed heartshaped deformation 86into a final fold F. Deforming dies 78, 84 and 90 strike against rimportion 16 of strip A while its bottom surface rests against support 94on a deforming machine. Deforming dies 78, 84 and 90 move downwardly tohave their bottom surfaces at varying spacing from bottom support 94 sothat fold F is progressively formed. In the final folding by deformingdie 90, the bottom surface of die 90 is spaced from bottom support 94 adistance greater than three times the thickness of metal in rim portion16. This produces a fold having smoothly curved bends.

An enlarged view of a fold F is shown in FIG. 16. As shown, rim portion16 includes planer portions 96 and 98 which extend between adjacentfolds. Fold F is symmetrical on opposite sides of a centerline 102 whichbisects fold F transversely of the sheet metal strip. As shown, fold Fis substantially S-shaped on the left side of centerline 102 and issubstantially backwards S-shaped on the right-hand side of centerline102. Fold F has first and second bends 104 and 106. Rim portion 16includes an upper surface 108 and a bottom surface 110. Interior curvedsurfaces 112 and 114 of first and second bends 104 and 106 are definedby portions of bottom surface 110 of rim portion 16. First and secondbends 104 and 106 have exterior curved surfaces 116 and 118 which aredefined by portions of upper surface 108 of rim portion 16. First andsecond bends 104 and 106 are connected by an upper web portion 122 whichextends substantially parallel to substantially planer portions 96 and98 of rim portion 16. Web portion 122 has inner and outer surfaces whichare defined respectively by portions of bottom surface 110 and uppersurface 108 of rim portion 16. Folds F include third and fourth bends124 and 126 having interior curved surfaces 128 and 130 facing inopposite directions and away from centerline 102. Interior curvedsurfaces 128 and 130 of third and fourth bends 124 and 126 are definedby portions of upper surface 108 of rim portion 16. Third and fourthbends 124 and 126 include exterior surfaces 132 and 134 facing oneanother and centerline 102, and being defined by portions of bottomsurface 110 of rim portion 16. It is important to note that a portion ofexterior curved surfaces 116 and 118 of first and second bends 104 and106 is in contact with substantially planer portions 96 and 98 as at 136and 138. Also, portions of exterior curved surfaces 132 and 134 of thirdand fourth bends 124 and 126 are in contact with the bottom surface ofweb 122 as at 140 and 142. In addition, it is important to note thatexterior curved surfaces 132 and 134 of third and fourth bends 124 and126 are spaced apart from one another. This spacing eliminates apreloaded joint so that the material is not under strain and there is noexpansion or contraction caused by relieving of metal stress as insituations where exterior curved surfaces 132 and 134 would be abuttingagainst one another. It is also important to note that all of bends 104,106, 124 and 126 are smoothly curved and interior curved surfaces 112,114, 128 and 130 are out of contact with one another over arcs greaterthan 180". With such an arrangement, there is minimum crystallization ofmetal at the bends, and work and age hardening are substantially reducedso that failure of the metal in any bend of fold F is substantiallyreduced. In one example for a strip to be used in making a 9 inchdiameter blower wheel, bend 64 is formed from sheet metal having athickness of around l/128 inch. With reference to FIG. 17, height 141 isaround 3/8 inches, width 143 around 1 H64 inches, radius 144 around 1/l6inches, and radii 146 and 148 around 3/32 inches. During the firstdeforming operation by deforming die 78 to make U-shaped bend 64 intoheart-shaped bend 82, the dimensions for a 9-inch-diameter blower wheelbecomes substantially as shown in FIG. 18. Width dimension 152 is around7/32 inches, width dimension 154 around 7/64 inches, height 156 around17/64 inches, interior radii 158 around l/32 inch and exterior radii 160around 1/16 inches. Heart-shaped deformation 82 is then further deformedby deforming die 86 into a deformed heart shape 86 as shown in FIG. 19.Height dimension 162 is then around 9/64 inches, width dimension 164around 17/64 inches and width dimension 166 around 3/64 inches. In finalfold F of FIG. 16, the spacing between exterior surfaces 132 and 134 ofthird and fourth bends 124 and 126 is around 1 /32 inches. This spacingis maintained for each fold formed in rim portion 16 and 18 by spacerelements 76 of FIG. 12. This insures substantially uniform longitudinalspacing of blade sections 30.

In accordance with another aspect of the present invention, blade stripA is formed into a cylinder in a manner more fully described in U.S.Pat. No. 3,423,012 issued Jan. 2], 1969, and copending U.S. Pat. No.application Ser. No. 789,675 filed .Ian. 8, 1969, which are assigned tothe same assignee as the present invention. With blade strip A arrangedin a cylinder, notches 28 in inner edges 44 of blade sections 30 arecircumferentially aligned. A pair of substantially identical discs Minclude substantially flat circular central portions having centrallylocated holes 182 therethrough for rotatably mounting discs M on ashaft. Discs M have circumferential converging portions 184 whichintersect at a circumferential contact area 186. Discs M includeoutwardly curved circumferential protuberances 188 which intersect at190 in a location spaced radially inward from diverging outer peripheraledges 192 of discs M. In previous arrangements, protuberances 188 weresmashed down to be substantially parallel to one another in order tocause diverging outer peripheral edges 192 to firmly engage the edges ofnotches 28. In accordance with the present invention, an apparatus ofthe type disclosed in the aforementioned copending application may beused to deform protuberances 188. However, instead of moving thedeforming dies extremely close to one another in order to deformprotuberances 188 into substantially parallel relationship, thedeforming die applies striking force as represented by arrows 200 whichbreaks protuberances 188 substantially at their centers to define acircumferential contact area 202 and to form two radially spacedprotuberances 204 and 206. Inner circumferential protuberance 204 has aninner circumferential edge corresponding with circumferential contactarea 186 and outer circumferential protuberance 206 has an outer edgecorresponding with circumferential contact area 188. Circumferentialcontact area 202 defines the inner circumferential edge of outerprotuberance 206 and the outer circumferential edge of innerprotuberance 204. Outer circumferential protuberances 206 are underbending 'stress between circumferential contact areas 188 and 202 whileinner circumferential protuberances 204 are under bending stress betweencircumferential contact areas 186 and 202. This bending stress firmlyholds outer peripheral edges 192 in firm engagement with notches 28 andprevents protuberances 204 or 206 from stress relieving over a longperiod of time. In previous arrangements, where protuberances weresimply deformed to be substantially parallel to one another, theflattened protuberances would relieve themselves of stress over a periodof time and the outer peripheral edges of the discs would become loosein the notches. With the arrangement of the present invention,protuberances 204 and 206 are in somewhat of a springlike arrangement sothat outer peripheral edges 192 are continuously biased into firmengagement with notches 28. This springlike action substantiallyeliminates relief of stress in the deformed metal which might cause theouter peripheral edges of discs M to become loose in notches 28. In onearrangement, with a Q-inch-diameter blower wheel and discs M having asheet metal thickness of around 1/64 inches, protuberances 204 and 206take the form shown in FIG. 22. Dimensions 214 and 216 are substantiallyequal at around 21/64 inches each. It will be understood that these areonly nominal dimensions and may vary by several 64ths of an inch. inaddition, it will be understood that dimensions given will vary withdifferent thicknesses of metal and different diameter blower wheels.

While the invention has been described with reference to preferredembodiments, it is obvious that modifications and alterations will occurto others upon the reading and understanding of this specification.

I claim:

1. A centrifugal blower wheel formed from a sheet metal strip havingopposite side edges, said strip having longitudinally spaced transverseblades formed therein between said side edges, said side edges includingmarginal rim portions extending continuously along said side edges ofsaid strip and integrally interconnecting said blades, said rim portionsincluding top and bottom surfaces and having folds therein betweenadjacent blades for decreasing the longitudinal spacing between saidblades, said rim portions including substantially planar portionsextending between adjacent folds, said folds being symmetrical onopposite sides of a centerline bisecting said folds transversely of saidstrip, said folds having a substantially S-shape on one side of saidcenterline and a substantially backwards S-shape on the other side ofsaid centerline, said folds including first and second bends havinginterior surfaces facing one another and said centerline, said interiorsurfaces of said first and second bends being defined by portions ofsaid bottom surface of said rim portions, said first and second bendshaving exterior surfaces defined by portions of said top surface of saidrim portions, said first and second bends being interconnected by anupper web portion of said folds extending substantially parallel to saidplanar portions of said rim portions, said web portion having inner andouter surfaces defined respectively by portions of said bottom and topsurfaces of said rim portions, said folds including third and fourthbends having interior surfaces facing in opposite directions and awayfrom said centerline, said interior'surfaces of said third and fourthbends being defined by portions of said top surface of said rimportions, said third and fourth bends having exterior surfaces facingone another and said centerline and being defined by portions of saidbottom surface of said rim portions, all of said interior surfaces ofsaid bends being smoothly curved and in spaced-apart noncontactingrelationship over arcs greater than 180.

2. The blower wheel of claim 1 wherein a portion of said exterior curvedsurfaces of said first and second bends are in contact with said topsurface of said rim portions at said planar portions thereof, and aportion of said exterior curved surfaces of said third and fourth bendsare in contact with said inner surface ofsaid web.

3. The blower wheel of claim 2 wherein said curved exterior surfaces ofsaid third and fourth bends are in spaced-apart relationshiplongitudinally of said strip.

4. The blower wheel of claim 1 wherein said curved exterior surfaces ofsaid third and fourth bends are in spaced-apart relationshiplongitudinally of said strip.

5. The blower wheel of claim 1 wherein said strip is formed into acylinder and said blades have inner and outer edges, said inner edgeshaving notch means formed therein, a pair of discs having outerperipheral edges, at least one of said edges on one of said discsdiverging away from said edge on the other of said discs, said one dischaving a pair of radially spaced inner and outer circumferentialprotuberances adjacent said outer peripheral edge, said innerprotuberance having an inner circumferential edge and said outerprotuberance having an outer circumferential edge positioned inwardly ofsaid diverging peripheral edge, said inner and outer protuberanceshaving a common circumferential edge defining an outer circumferentialedge of said inner protuberance and an inner circumferential edge ofsaid outer protuberance, said circumferential edges of saidprotuberances on said one disc being in contact with said other disc,said inner and outer protuberances being under bending and compressiveforces, said forces holding said diverging peripheral edges in biasedengagement with said notch means and said circumferential edges of saidprotuberances in engagement with said other disc.

6. The blower wheel of claim 5 wherein said blades are deformed out ofthe plane of said strip and have an arcuate cross-sectional shape ofpredetermined arcuate length, said blades having end portions integrallyconnected with said rim portions by connecting webs, said webs having awidth longitudinally of said strip substantially less than saidpredetermined arcuate length, said end portions of said blades adjacentsaid webs being work hardened less than the intermediate portion of saidblades between said end portions.

7. The blower of claim 1 wherein said blades are deformed out of theplane of said strip and have an arcuate cross-sectional shape ofpredetermined arcuate length, said blades having end portions integrallyconnected with said rim portions by connecting webs, said webs having awidth longitudinally of said strip substantially less than saidpredetermined arcuate length, said end portions of said blades adjacentsaid webs being work hardened less than the intermediate portion of saidblades between said end portions.

8. A centrifugal blower wheel comprising a cylindrical blade striphaving a longitudinal axis, said strip including a plurality ofcircumferentially spaced blades extending substantially parallel to saidlongitudinal axis, said blades having inner and outer edges, said inneredges having notch means formed therein, a pair of discs having outerperipheral edges, at least one of said edges on one of said discsdiverging away from said edge on the other of said discs, said one dischaving a pair of radially spaced inner and outer circumferentialprotuberances adjacent said outer peripheral edge, said innerprotuberance having an inner circumferential edge and said outerprotuberance having an outer circumferential edge positioned inwardly ofsaid diverging peripheral edge, said inner and outer protuberanceshaving a common circumferential edge defining an outer circumferentialedge of said inner protuberance and an inner circumferential edge ofsaid outer protuberance, said circumferential edges of saidprotuberances on said one disc being in contact with said other disc,said inner and outer protuberances being under bending and compressiveforces, said forces holding said diverging peripheral edge in biasedengagement with said notch means and said circumferential edges of saidprotuberances in engagement with said other disc.

9. The blower wheel of claim 8 wherein said other disc is substantiallyidentical to said one disc and has an outer peripheral edge divergingfrom said one disc and a pair of inner and outer circumferentialprotuberances having circumferential edges corresponding to saidcircumferential edges of said inner and outer protuberances on said onedisc, said circumferential edges of said protuberances on said otherdisc being in contact with said circumferential edges of saidprotuberances on said one disc, said protuberances on said other discbeing under bending and compressive forces, said forces holding saiddiverging peripheral edge of said other disc in biased engagement withsaid notch means and said circumferential edges of said protuberances ofsaid other disc in engagement with said circumferential edges of saidprotuberances of said one disc.

10. A sheet metal blade strip for centrifugal blower wheels, said striphaving opposite side edges, said strip having longitudinally spacedtransverse bla-lcs formed therein between said side edges, said sideedges including marginal rim portions extending continuously along saidside edges of said strips and integrally interconnecting said blades,said blades being deformed out of the plane of said strip and having anarcuate cross-sectional shape of predetermined arcuate length, saidblades having end portions integrally connected with said rim portionsby connecting webs, said webs having a width longitudinally of saidstrip substantially less than said predetermined arcuate length, saidend portions of said blades adjacent said web being work hardened lessthan the intermediate portion of said blades between said end portions.

11. A method of forming a blade strip for a centrifugal blower wheelfrom a sheet metal strip having opposite side edges comprising the stepsof; punching longitudinally spaced arcuate blades into said striptransversely thereof between said side edges to provide marginal rimportions extending continuously along said side edges of said stripintegrally interconnecting the end portions of the blades, deformingsaid rim portions into an inverted U-shape deformation, striking thearcuate portion of said deformation and bending the arcuate portion ofsaid deformation at its center to form a substantially heart-shapeddeformation, and striking said heart-shaped deformation between surfaceswhich close to a spacing greater than three times the thickness of saidrim portions to flatten said heart-shaped deformation into a fold havingbends which are smoothly curved.

12. A method of assembling a centrifugal blower wheel from a cylindricalblade strip having a plurality of circumferentially spaced blades withnotch means in their inner edges, and from a pair of discs having outerperipheral edges and circumferential arcuate protuberances spacedradially in- I ward from said outer peripheral edges, comprising thesteps of; positioning said outer peripheral edges of said discs in saidnotch means, and striking said protuberances to bend said protuberancestoward one another around the center portions thereof and provide a pairof radially spaced arcuate protuberances in each of said discs which areunder bending and compressive stress to firmly bias said outerperipheral edges into engagement with said notch means.

13. A method of deforming curved blower blades from a sheet metal striphaving opposite side edges including marginal rim portions extendingcontinuously along said strips, said strip having longitudinally spacedtransverse slits formed therein between said side edges, said striphaving generally longitudinal slits formed therein extending along saidrim portions from each end of said transverse slits toward an adjacentslit, said slits defining substantially rectangular blade formingsections connected with said rim portions by webs defined betweenadjacent longitudinal slits, comprising the steps of; initially strikingthe major portion of said blade-forming sections to impart initialcurvature thereto while leaving the end portions of said blade-formingsections adjacent said webs substantially flat, and subsequentlystriking said blade-forming sections to impart further curvature theretoand to curve the end portions of said blade-forming sections adjacentsaid webs whereby the end portions of said blade-forming sections arework hardened less than when they are repeatedly curved in a pluralityof successive striking steps.

1. A centrifugal blower wheel formed from a sheet metal strip havingopposite side edges, said strip having longitudinally spaced transverseblades formed therein between said side edges, said side edges includingmarginal rim portions extending continuously along said side edges ofsaid strip and integrally interconnecting said blades, said rim portionsincluding top and bottom surfaces and having folds therein betweenadjacent blades for decreasing the longitudinal spacing between saidblades, said rim portions including substantially planar portionsextending between adjacent folds, said folds being symmetrical onopposite sides of a centerline bisecting said folds transversely of saidstrip, said folds having a substantially S-shape on one side of saidcenterline and a substantially backwards S-shape on the other side ofsaid centerline, said folds including first and second bends havinginterior surfaces facing one another and said centerline, said interiorsurfaces of said first and second bends being defined by portions ofsaid bottom surface of said rim portions, said first and second bendshaving exterior surfaces defined by portions of said top surface of saidrim portions, said first and second bends being interconnected by anupper web portion of said folds extending substantially parallel to saidplanar portions of said rim portions, said web portion having inner andouter surfaces defined respectively by portions of said bottom and topsurfaces of said rim portions, said folds including third and fourthbends having interior surfaces facing in opposite directions and awayfrom said centerline, said interior surfaces of said third and fourthbends being defined by portions of said top surface of said rimportions, said third and fourth bends having exterior surfaces facingone another and said centerline and being defined by portions of saidbottom surface of said rim portions, all of said interior surfaces ofsaid bends being smoothly curved and in spaced-apart noncontactingrelationship over arcs greater than 180*.
 2. The blower wheel of claim 1wherein a portion of said exterior curved surfaces of said first andsecond bends are in contact with said top surface of said rim portionsat said planar portions thereof, and a portion of said exterior curvedsurfaces of said third and fourth bends are in contact with said innersurface of said web.
 3. The blower wheel of claim 2 wherein said curvedexterior surfaces of said third and fourth bends are in spaced-apartrelationship longitudinally of said strip.
 4. The blower wheel of claim1 wherein said curved exterior surfaces of said third and fourth bendsare in spaced-apart relationship longitudinally of said strip.
 5. Theblower wheel of claim 1 wherein said strip is formed into a cylinder andsaid blades have inner and outer edges, said inner edges having notchmeans formed therein, a pair of discs having outer peripheral edges, atleast one of said edges on one of said discs diverging away from saidedge on the other of said discs, said one disc having a pair of radiallyspaced inner and outer circumferential protuberances adjacent said outerperipheral edge, said inner protuberance having an inner circumferentialedge and said outer protuberance having an outer circumferential edgepositioned inwardly of said diverging peripheral edge, said inner andouter protuberances having a common circumferential edge defining anouter circumferential edge of said inner protuberance and an innercircumferential edge of said outer protuberance, said circumferentialedges of said protuberances on said one disc being in contact with saidother disc, said inner and outer protuberances Being under bending andcompressive forces, said forces holding said diverging peripheral edgesin biased engagement with said notch means and said circumferentialedges of said protuberances in engagement with said other disc.
 6. Theblower wheel of claim 5 wherein said blades are deformed out of theplane of said strip and have an arcuate cross-sectional shape ofpredetermined arcuate length, said blades having end portions integrallyconnected with said rim portions by connecting webs, said webs having awidth longitudinally of said strip substantially less than saidpredetermined arcuate length, said end portions of said blades adjacentsaid webs being work hardened less than the intermediate portion of saidblades between said end portions.
 7. The blower of claim 1 wherein saidblades are deformed out of the plane of said strip and have an arcuatecross-sectional shape of predetermined arcuate length, said bladeshaving end portions integrally connected with said rim portions byconnecting webs, said webs having a width longitudinally of said stripsubstantially less than said predetermined arcuate length, said endportions of said blades adjacent said webs being work hardened less thanthe intermediate portion of said blades between said end portions.
 8. Acentrifugal blower wheel comprising a cylindrical blade strip having alongitudinal axis, said strip including a plurality of circumferentiallyspaced blades extending substantially parallel to said longitudinalaxis, said blades having inner and outer edges, said inner edges havingnotch means formed therein, a pair of discs having outer peripheraledges, at least one of said edges on one of said discs diverging awayfrom said edge on the other of said discs, said one disc having a pairof radially spaced inner and outer circumferential protuberancesadjacent said outer peripheral edge, said inner protuberance having aninner circumferential edge and said outer protuberance having an outercircumferential edge positioned inwardly of said diverging peripheraledge, said inner and outer protuberances having a common circumferentialedge defining an outer circumferential edge of said inner protuberanceand an inner circumferential edge of said outer protuberance, saidcircumferential edges of said protuberances on said one disc being incontact with said other disc, said inner and outer protuberances beingunder bending and compressive forces, said forces holding said divergingperipheral edge in biased engagement with said notch means and saidcircumferential edges of said protuberances in engagement with saidother disc.
 9. The blower wheel of claim 8 wherein said other disc issubstantially identical to said one disc and has an outer peripheraledge diverging from said one disc and a pair of inner and outercircumferential protuberances having circumferential edges correspondingto said circumferential edges of said inner and outer protuberances onsaid one disc, said circumferential edges of said protuberances on saidother disc being in contact with said circumferential edges of saidprotuberances on said one disc, said protuberances on said other discbeing under bending and compressive forces, said forces holding saiddiverging peripheral edge of said other disc in biased engagement withsaid notch means and said circumferential edges of said protuberances ofsaid other disc in engagement with said circumferential edges of saidprotuberances of said one disc.
 10. A sheet metal blade strip forcentrifugal blower wheels, said strip having opposite side edges, saidstrip having longitudinally spaced transverse blades formed thereinbetween said side edges, said side edges including marginal rim portionsextending continuously along said side edges of said strips andintegrally interconnecting said blades, said blades being deformed outof the plane of said strip and having an arcuate cross-sectional shapeof predetermined arcuate length, said blades having end portionsintegrally connected with said rim porTions by connecting webs, saidwebs having a width longitudinally of said strip substantially less thansaid predetermined arcuate length, said end portions of said bladesadjacent said web being work hardened less than the intermediate portionof said blades between said end portions.
 11. A method of forming ablade strip for a centrifugal blower wheel from a sheet metal striphaving opposite side edges comprising the steps of; punchinglongitudinally spaced arcuate blades into said strip transverselythereof between said side edges to provide marginal rim portionsextending continuously along said side edges of said strip integrallyinterconnecting the end portions of the blades, deforming said rimportions into an inverted U-shape deformation, striking the arcuateportion of said deformation and bending the arcuate portion of saiddeformation at its center to form a substantially heart-shapeddeformation, and striking said heart-shaped deformation between surfaceswhich close to a spacing greater than three times the thickness of saidrim portions to flatten said heart-shaped deformation into a fold havingbends which are smoothly curved.
 12. A method of assembling acentrifugal blower wheel from a cylindrical blade strip having aplurality of circumferentially spaced blades with notch means in theirinner edges, and from a pair of discs having outer peripheral edges andcircumferential arcuate protuberances spaced radially inward from saidouter peripheral edges, comprising the steps of; positioning said outerperipheral edges of said discs in said notch means, and striking saidprotuberances to bend said protuberances toward one another around thecenter portions thereof and provide a pair of radially spaced arcuateprotuberances in each of said discs which are under bending andcompressive stress to firmly bias said outer peripheral edges intoengagement with said notch means.
 13. A method of deforming curvedblower blades from a sheet metal strip having opposite side edgesincluding marginal rim portions extending continuously along saidstrips, said strip having longitudinally spaced transverse slits formedtherein between said side edges, said strip having generallylongitudinal slits formed therein extending along said rim portions fromeach end of said transverse slits toward an adjacent slit, said slitsdefining substantially rectangular blade forming sections connected withsaid rim portions by webs defined between adjacent longitudinal slits,comprising the steps of; initially striking the major portion of saidblade-forming sections to impart initial curvature thereto while leavingthe end portions of said blade-forming sections adjacent said webssubstantially flat, and subsequently striking said blade-formingsections to impart further curvature thereto and to curve the endportions of said blade-forming sections adjacent said webs whereby theend portions of said blade-forming sections are work hardened less thanwhen they are repeatedly curved in a plurality of successive strikingsteps.